Must be something you're doing because I can add up to 3hrs to my series links.
Yes, but only on a individual basis.
All of my overlaps are set to 4 minutes as standard and I never miss the end of recordings.
The only exception to this was a series of Scooby Doo that the kids wanted, changed the series link I needed to and done. No need to do them all at once.
What's that got to do with my op?
It answers your op. You wanted to add longer padding, I've told you how to do it.